Abstract
BackgroundVaginal lactobacilli protect the female genital tract by producing lactic acid, bacteriocins, hydrogen peroxide or a local immune response. In bacterial vaginosis, normal lactobacilli are replaced by an anaerobic flora and this may increase susceptibility to Neisseria gonorrhoeae, a facultative anaerobe. Bacterial interference between vaginal lactobacilli and N. gonorrhoeae has not been studied in liquid medium under anaerobic conditions. By co-cultivating N. gonorrhoeae in the presence of lactobacilli we sought to identify the relative contributions of acidification and hydrogen peroxide production to any growth inhibition of N. gonorrhoeae.MethodsThree strains of N. gonorrhoeae distinguishable by auxotyping were grown in the presence of high concentrations (107-108 cfu/mL) of three vaginal lactobacilli (L. crispatus, L. gasseri and L. jensenii) in an anerobic liquid medium with and without 2-(N-morpholino)-ethanesulfonic (MES) buffer. Fusobacterium nucleatum was used as an indicator of anaerobiosis. Bacterial counts were performed at 15, 20 and 25 h; at 25 h pH and hydrogen peroxide concentrations were measured.ResultsGrowth of F. nucleatum to >108 cfu/mL at 25 h confirmed anaerobiosis. All bacteria grew in the anaerobic liquid medium and the addition of MES buffer had negligible effect on growth. L. crispatus and L. gasseri produced significant acidification and a corresponding reduction in growth of N. gonorrhoeae. This inhibition was abrogated by the addition of MES. L. jensenii produced less acidification and did not inhibit N. gonorrhoeae. Hydrogen peroxide was not detected in any experiment.ConclusionsDuring anaerobic growth, inhibition of N. gonorrhoeae by the vaginal lactobacilli tested was primarily due to acidification and abrogated by the presence of a buffer. There was no evidence of a specific mechanism of inhibition other than acid production under these conditions and, in particular, hydrogen peroxide was not produced. The acidification potential of vaginal lactobacilli under anaerobic conditions may be their most important characteristic conferring protection against N. gonorrhoeae infection.
Highlights
Vaginal lactobacilli protect the female genital tract by producing lactic acid, bacteriocins, hydrogen peroxide or a local immune response
The medium was sterilized through a 0.22 μ filter (Nalgene) and 7 mL volumes added to 7 mL screw-top plastic bijoux (Sterilin) giving a headspace above the liquid in each bijoux of approximately 1 mL
The LB studied here include representatives of the three species most frequently recovered from the healthy premenopausal vagina: L. crispatus, L. gasseri and L. jensenii
Summary
Vaginal lactobacilli protect the female genital tract by producing lactic acid, bacteriocins, hydrogen peroxide or a local immune response. Normal lactobacilli are replaced by an anaerobic flora and this may increase susceptibility to Neisseria gonorrhoeae, a facultative anaerobe. The majority of healthy women harbor lactobacilli (LB) in the vagina at counts of 107-109 cfu/gm secretions [1,2]. These protect the female genital tract by metabolising glycogen in shed epithelial cells to produce lactic acid, thereby generating a low pH environment. The hallmark of bacterial vaginosis (BV) - a highly prevalent condition of global public health importance is replacement of normal vaginal LB by a mixed flora of anaerobic bacteria. Studies suggest that an abnormal vaginal flora increases susceptibility to infection with sexually-transmitted pathogens including Neisseria gonorrhoeae (NG)
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